Renal failure is a major cause of morbidity and mortality in shock. There is a dissociation between total renal blood flow and tubular function during shock, and adrenergic agents are known to be able to dissociate these factors under normal conditions. It is presumed that a combination of adrenergic stimulating and blocking agents can reverse the detrimental ischemic effects of shock upon the kidney. The rat and dog differ markedly in their vulnerability to shock for reasons which are unclear. Responsiveness to adrenergic agents in these animals may shed light on this vulnerability difference and suggest a way to confirm resistance to renal failure in shock. A humoral factor responsible for shock in the vulnerable dog will be tested for its effect in the resistant rat.